Positron emission tomography (PET) is a functional imaging modality used in both clinical and laboratory settings. A PET image can show the distribution of a tracer throughout a subject's body. The tracer can be labeled with a radionuclide that emits positrons upon decay. The positrons can contact electrons and annihilate and produce pairs of 511 keV photons traveling in opposite directions. A PET scanner can detect coincident photons arising arise from the same annihilation and store these coincident events in arrays corresponding to projections through the subject's body or in a list of information specifying each event (“list mode”). A PET image can be reconstructed using standard tomographic techniques to reveal the function of various tissues (e.g., cells, organs, tissues, etc.) of a subject's body within the field of view of the PET scanner.
The functions that can be revealed in the PET image can be dependent on the spatial resolution of the PET scanner, which can be determined based on the ability of detectors within the PET scanner to locate a detected event. Clinical PET scanners designed to image human subjects can produce images with a spatial resolution of about 4.5 cm. While such a spatial resolution is generally acceptable for most clinical applications, it can be insufficient for some clinical applications requiring high spatial resolution in a focused region of interest (e.g. prostate imaging or breast imaging). This spatial resolution is often unacceptable for laboratory research, especially research involving small animals (e.g., rodents). Accordingly, dedicated small animal PET scanners have been developed for laboratory research applications using special higher-resolution detectors to achieve a spatial resolution of about 1.5 mm. However, such small animal PET scanners can be prohibitively expensive and require additional facilities.